First of all congratz on starting your journey. It's hard to estimate how long things will take because it really depends on your lifestyle.
For me it took 2-3 months to where I could comfortably go about my routine in the city. About 6 months in people really started to be impressed and most would continue the conversation in Thai. Im now 8 months in and in a weird stage of understanding a lot but also misunderstanding a lot. To my farang peers, I speak Thai, but really I'm far from being as fluent as I want to be.
My methods were:
1. Daily vocab and phrases flashcards on my phone (Anki app)
2. Watching a lot of unsubtitled Thai media
3. Speaking to everyone I could about anything
You can probably learn to read in as little as 7 tortuous days. I chose the lazy route and just memorized the consonants/vowels, then brute forced my way through text messages, menus, and signs based on context.
some random tips:
1. Really focus hard on tones, just don't be frustrated that it takes a while. It took me probably 4 months to "get it". I honestly think tones are more important than constants. I garble a lot of consonants but never ever tones and am understood well.
2. Record yourself on your phone and listen back. It's a very humbling experience but worth it.
3. Try shadowing media you consume. This means repeating back what is said as best as you can. This will feel impossible at first but just keep doing it.
4. I would recommend getting a private tutor over a group class, other students will just hold you back.